Field of the Invention
Published European Patent Application EP 0 734 059 A2 discloses a so-called chip-size semiconductor device, that is to say a semiconductor device in chip format, which is distinguished by the fact that its areal dimensions essentially corresponds to those of the chip, and it is larger than the chip only in terms of height. In the known semiconductor device, the external connections are fitted above the surface of the actual chip by the chip having on a surface, in addition to a passivation layer, a first insulating layer and electrical connection pads free of the insulating layers. The electronics disposed within the chip are electrically connected to the electrical connection pads. Interconnects which proceed from the electrical connection pads and end at base points of external connection elements run on the first insulating layer. In the known semiconductor device, the external connection elements are formed in each case by a solder ball which extends through an opening in a further insulating layer as far as the interconnect, where it has its base point. In this case, the external connection elements in the form of the solder balls are disposed in a manner corresponding to the grid of soldering points on a printed circuit board. The known semiconductor device can therefore be applied to a printed circuit board in a straightforward manner by soldering.
It is accordingly an object of the invention to provide a semiconductor device in chip format and a method for producing it that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, that enables comparatively good mechanical decoupling from a printed circuit board when the semiconductor component is soldered onto the printed circuit board.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor device in chip format. The device is formed of a chip, electrical connection pads disposed on the chip, and at least one first insulating layer disposed on the chip such that the electrical connection pads are free of the first insulating layer on at least one surface. Interconnects run on the first insulating layer and in each case lead from the electrical connection pads to base regions. A second insulating layer is disposed on the interconnects and on the first insulating layer. The second insulating layer is thicker than the first insulating layer. The second insulating layer has openings formed therein and each of the openings leads to a respective one of the base regions. Cylinders made of a cured, elastic conductive adhesive material are disposed in each of the openings. Small plastic balls having a metallic coating on an outside are disposed in each case on a respective one of the cylinders made of the cured, elastic conductive adhesive material in a region of a free end of each of the openings.
In accordance with an added feature of the invention, the second insulating layer is at least four times thicker than the first insulating layer.
An essential advantage of the semiconductor device according to the invention results from the conductive adhesive introduced into the openings in the second insulating layer. Such a conductive adhesive has comparatively good elastic properties even after it has been cured, so that, for example as a result of heating of a composite formed from a printed circuit and the semiconductor device, with accompanying varying thermal stresses, the stresses are kept away from the connecting points between the semiconductor device and the printed circuit board. Additionally, the cured conductive adhesive has a comparatively good aging behavior under mechanical alternating load.
In an advantageous refinement of the semiconductor device according to the invention, the second insulating layer is made considerably thicker than the at least one first insulating layer. This affords the advantageous possibility of filling a relatively large amount of conductive adhesive into the opening. As a result of which, after curing, relatively long cylinders are formed from the conductive adhesive material, which advantageously contribute to the good mechanical decoupling from a printed circuit board connected to the semiconductor device by soldering.
In a particularly advantageous embodiment of the semiconductor device according to the invention, the small balls that are metallic at least on the outside are metallized small plastic balls. Small balls of this type are distinguished by high elasticity, so that they make quite a substantial contribution to the mechanical decoupling of the semiconductor device from a printed circuit board populated with the semiconductor device. From U.S. Pat. No. 5,477,087 it is known per se to use connection elements having a plastic core with a metal coating in order to connect semiconductor devices to printed circuit boards. However, these connection elements are connected to the connection pad of the chip by a metal layer.
Another way of achieving the object specified above consists, according to the invention, in a semiconductor device in chip format having a chip which has, on at least one surface, at least one first insulating layer and electrical connection pads free of the insulating layer. The chip is furthermore provided with interconnects running on the first insulating layer. The interconnects in each case lead from the electrical connection pads to base regions of external connection elements, with a second insulating layer situated on the interconnects and on the at least one first insulating layer. The second insulating layer has, above the respective base region, an opening with introduced solder paste, and with metallized small plastic balls which are in each case placed onto the solder paste in the region of the free end of the via openings.
This embodiment is also distinguished by good mechanical decoupling properties between a printed circuit board and the soldered-on semiconductor device according to the invention, which can be attributed to the use of the metallized small plastic balls. This is because the small plastic balls have comparatively good elastic properties and therefore absorb the mechanical stresses between the printed circuit board and the semiconductor element.
In this embodiment, too, it is regarded as advantageous if the second insulating layer is considerably thicker than the at least one insulating layer, because the remelted solder paste forms a comparatively long cylinder with the metallized small plastic ball at its end, which contributes to a good mechanical decoupling between printed circuit board and semiconductor device.
The invention is furthermore based on the object of specifying a method for producing a semiconductor device in chip format which can be used to produce, in a comparatively simple manner, semiconductor devices having good mechanical decoupling properties.
One way in which this object is achieved consists in a method in which at least one first insulating layer is applied to at least one surface of the chip, with electrical connection pads being left free. Interconnects leading to a respective base region of external connection elements are applied to the at least one first insulating layer. On the interconnects and on the at least one first insulating layer, provision is made of a second insulating layer with openings above the respective base region. A conductive adhesive is introduced into the openings, small plastic balls that are metallic at least on the outside are in each case placed onto the conductive adhesive in the region of the free end of the openings, and the conductive adhesive is cured.
An essential advantage of the method according to the invention is that it can be used to produce semiconductor devices with mechanical decoupling properties in a comparatively simple manner because the step of introducing a conductive adhesive into the openings in the second insulating layer and also the step of placing small balls which are metallic at least on the outside onto the conductive adhesive can be carried out comparatively simply in process engineering terms.
Another embodiment of the method according to the invention consists in a method in which at least one first insulating layer is applied to at least one surface of the chip, with electrical connection pads being left free. Interconnects leading to a respective base region of external connection elements are applied to the at least one first insulating layer. On the interconnects and on the at least one first insulating layer, provision is made of a second insulating layer with openings above the respective base region. Solder paste is introduced into the openings, small plastic balls which are metallized on the outside are in each case placed onto the solder paste in the region of the free end of the via openings, and the solder paste is remelted.
The methods according to the invention can be carried out particularly simply when the conductive adhesive or the solder paste is introduced into the openings using a doctor blade, because introduction by a doctor blade is a comparatively simple process step. However, the introduction of solder paste by a doctor blade is already known per se, as revealed in the published Japanese Patent Application 6-232134, which is dealt with in the documentation xe2x80x9cFlip-Chip-Technology, Vol. VII-1995 Update Foreign Patentsxe2x80x9d, published in International Interconnection Intelligence, page 256.
The method according to the invention can be carried out particularly advantageously when the method steps are carried out on a wafer, and after the curing of the conductive adhesive or the remelting of the solder paste, the wafer is divided to obtain the semiconductor devices.
This leads to a significant reduction of costs because the individual method steps are not carried out individually for each chip but rather, to an extent, in the chip composite constituted by a wafer.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor device in chip format and a method for producing it, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.